Method for manufacturing stainless steel ball stud for automotive suspension system

ABSTRACT

Provided is a method for manufacturing a stainless steel ball stud for an automotive suspension system, which includes: a forging and molding step of forging and molding a cylindrical shaped stainless material blank with the same top and bottom diameters by using a progressive press machine to operate a number of mold dies simultaneously and to move a forged mold product of a preceding die to a succeeding die, to make a forged mold product; a male thread shaping step of shaping a male thread on the forged mold product; and a cutting and surface finishing/burnishing step of cutting the forged mold product by using one ball stud processing machine such that a head part is cut at exact dimensions, a neck part and a washer part are shaped and the surface finishing/burnishing work to the head part is performed to complete the stainless steel ball stud for an automotive suspension system.

TECHNICAL FIELD

The present invention relates to a method for manufacturing a stainless steel ball stud for an automotive suspension system and more particularly, to a method for manufacturing a stainless steel ball stud for an automotive suspension system, whereby a forged stainless mold product made at a forging step is manufactured as a high quality stainless suspension ball stud through a male thread shaping step, a cutting step and a surface finishing/burnishing step.

BACKGROUND ART

In general, a vehicle has not only an impact from the road surface but also the vibrations including bump bouncing which is a vibration in the vertical direction of the vehicle, lurching which is a vibration in the transverse (side to side) direction of the vehicle, surging which vibrates in the longitudinal (forward and backward) direction of the vehicle, yawing which rotates around the vertical axis, pitching which rotates around the transverse axis, rolling which rotates around the longitudinal axis.

To absorb a vibration occurring from the road surface, a suspension system is installed to primarily alleviate the vibration through wheels and absorb the high vibration transferred through the wheels, thereby suppressing the shaking of the vehicle body and improving the ride comport.

An automotive suspension system connects a vehicle to its wheels, supports an external force, which acts in the vertical direction, by using a spring and a shock absorber and properly harmonizes high rigidity and flexibility in the other directions, to mechanically properly harmonize the relative motion between the vehicle body and the wheels.

In the automotive suspension system, a lower arm, a knuckle and a stabilizer link are connected by ball studs.

A ball stud for an automotive suspension system is manufactured by heat-treating and annealing a structure steel; cold forging the steel to make a mold product with a head part, a washer part, a tapered part, a thread process part and a hexagonal socket; quenching the forged mold product; heat-treating it by tempering to improve its intensity; forming a male thread on the thread process part; and cutting the head part and neck part.

Ball studs for an automotive suspension system are designed in various shapes. Specifically, only when a forged mold product is shaped by using a proper process for its design shape at the forging and molding step, the fatigue degree of a mold die is reduced to extend the life of the mold die, and the processing burden at the cutting step is reduced to improve productivity and to save cost.

FIG. 1 is a front view of a stainless steel ball stud 10 for an automotive suspension system which is related to the present invention.

The ball stud 10 includes a head part 11 in a ball shape, a recessed neck part 12 under the head part 11, a washer part 13 at a lower end of the neck part 12, a straight line part 14 under the washer part 13 and having a smaller diameter than the washer part 13, a tapered part 15 under the straight line part 14 and having a diameter which gradually becomes smaller downwardly, a male thread part 16 under the tapered part 15 and having a smaller diameter than the lower end of the tapered part 15, dog point part 17 under the male thread part 16 and having a smaller diameter than the male thread part 16, and a hex socket 18 formed into the bottom of the dog point part 17.

Patent Document 1 (Korean Application Publication No. 10-2008-0114219) discloses a method for molding a ball stud for a stabilizer link used in an automotive suspension system, in which the ball stud is molded by cool forging.

According to the method for molding a ball stud for a stabilizer link in Patent Document 1, a forged mold product of the ball stud is molded after cool forging. However, the method of this patent document is to manufacture a ball stud in a different shape which does not include the tapered part of the stainless steel ball stud for an automotive suspension system related to the present invention. Therefore, the method according to this patent document cannot mold a forged mold product to manufacture the stainless steel ball stud for the automotive suspension system related to the present invention.

Patent Document 2 (Japanese Patent Publication No. Hei 6-88096) discloses a method for manufacturing a ball stud in a similar shape to a stainless steel ball stud for an automotive suspension system related to the present invention.

According to Patent Document 2, the method is to manufacture a ball stud in which a washer part is positioned under a neck part and a straight line part, a tapered part and thread part are positioned under the washer part. The forged mold product is molded through the forging and molding step with 1^(st) to 6^(th) molding processes.

In the method of Patent Document 2, since a molding process to form a hex socket is not included at the forging and molding step, the hex socket needs to be post-processed at the bottom of the thread part after the forging and molding step.

Further, according to the method of Patent Document 2, since the tapered part is modified in the other molding processes except for the 1^(st) molding process, the surface of the tapered part is irregular. Therefore, to obtain high precision, the tapered part needs to be cut and processed at the cutting step after the forging and molding step.

DISCLOSURE Technical Problem

As described above, the methods for manufacturing a ball stud according to the conventional art including Patent Documents 1 and 2 are unable to obtain a forged mold product which is proper for manufacturing a stainless steel ball stud for an automotive suspension system related to the present invention.

Further, in the methods for manufacturing a ball stud according to the conventional art, since many parts of a forged mold product need to be cut or post-processed, productivity drops and manufacturing costs are high.

Further, in the methods for manufacturing a ball stud according to the conventional art, since a ball stud is made of structural steel requiring heat-treatment, it needs a heat-treatment step and a plating step for corrosion proof. Therefore, manufacturing processes are complicated, so that a lot of manufacturing time, manufacturing manpower and manufacturing costs are required and productivity drops.

Therefore, it is an object of the present invention to solve the above problems and to provide a method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the ball stud is shaped with a ball-shaped head part, a recessed neck part under the head part, a washer part at a lower end of the neck part, a straight line part under the washer part and having a smaller diameter than the washer part, a tapered part under the straight line part and having a diameter which gradually becomes smaller downwardly, a male thread part under the tapered part and having a smaller diameter than the lower end of the tapered part, a dog point part under the male thread part and having a smaller diameter than the male thread part, and a hex socket formed into the bottom of the dog point part.

It is another object of the present invention to provide a method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the most proper forged mold product for manufacturing the ball stud is manufactured at a forging and molding step.

It is another object of the present invention to provide a method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the surface of the head part is finished/burnished by using one ball stud processing machine used to cut the head part and the neck part, following the process of cutting the head part and the neck part, thereby improving productivity.

It is another object of the present invention to provide a method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the heat-treatment step or plating step is not required, i.e. may be skipped, to improve productivity and to reduce manufacturing costs.

Technical Solution

In accordance with an embodiment of the present invention, there is provided a method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the stainless steel ball stud is shaped with a head part in a ball shape, a recessed neck part under the head part, a washer part at a lower end of the neck part, a straight line part under the washer part and having a smaller diameter than the washer part, a tapered part under the straight line part and having a diameter which gradually becomes narrower downwardly, a male thread part under the tapered part and having a smaller diameter than the lower end of the tapered part, a dog point part under the male thread part and having a smaller diameter than the male thread part, and a hex socket formed into a bottom of the dog point part, the method comprising: a forging and molding step of forging and molding a cylindrical shaped stainless material blank with the same top and bottom diameters by using a progressive press machine to operate a number of mold dies simultaneously and to move a forged mold product of a preceding die to a succeeding die, to make a forged mold product; a male thread shaping step of shaping a male thread on the forged mold product; and a cutting and surface finishing/burnishing step of cutting the forged mold product by using one ball stud processing machine such that the head part is cut at exact dimensions, the neck part and the washer part are shaped and the surface finishing/burnishing work to the head part is performed to complete the stainless steel ball stud for an automotive suspension system.

The forging and molding step manufactures the forged mold product which is shaped with a ball-shaped head part, a pre-neck part arranged in a vertical shape under the ball-shaped head part, a vertical part under the pre-neck part and having a smaller diameter than the pre-neck part, a tapered part under the vertical part and having a diameter which becomes gradually narrower downwardly, a pre-male thread part under the tapered part and having a smaller diameter than a lower end of the tapered part, a dog point part under the pre-male thread part and having a smaller diameter than the pre-male thread part, and a hex socket at the bottom of the dog point part.

The forging and molding step comprises a six (6)-step molding process such that the cut material is moved to a first mold die, a first mold product is moved to a second mold die, a second mold product is moved to a third mold die, a third mold product is moved to a fourth mold die, a fourth mold product is moved to a fifth mold die, a fifth mold product is moved to a sixth mold die, and a sixth mold product is discharged to the outside.

The forging and molding step comprises: a first molding process to mold, in a first mold die, a first mold product that includes the generally vertical part with a top and bottom having the same diameter, and a rounded bottom end with a smaller diameter, by using the material blank of a certain length which has a top end and a bottom end with the same diameter; a second molding process to mold, in a second mold die, a second mold product in which the pre-male thread part positioned at a lower section of the vertical part is in a vertical shape with a smaller diameter than the vertical part and the vertical part is connected to the pre-male thread part in a hemispheric shape, by using the first mold product; a third molding process to mold, in a third mold die, a third mold product in which a pre-head part, which is tapered to have an upper end with a greater diameter than a lower end, and the pre-neck part, which is in a vertical shape with a greater diameter than the vertical part, are positioned in an upper section of the vertical part, and the pre-head part and the pre-neck part are connected to be tapered such that a diameter becomes narrower downwardly, by using the second mold product; a fourth molding process to mold, in a fourth mold die, a fourth mold product in which the ball-shaped head part is shaped in the pre-head part, the dog point part in a vertical shape with a smaller diameter than the pre-male thread part is shaped in a lower section of the pre-male thread part and a pre-hex socket part is shaped at a lower end of the dog point part, by using the third mold product; a fifth molding process to mold, in a fifth mold die, a fifth mold product in which the hex socket is shaped at the lower end of the dog point part, by using the fourth mold product; and a sixth molding process to mold, in a sixth mold die, a sixth mold product in which the tapered part is shaped in a lower section of the vertical part, by using the fifth mold product.

The cutting and surface finishing/burnishing step comprises: a first cutting process to cut the ball-shaped head part of the forged mold product at exact dimensions to shape the head part by using a first cutter of the ball stud processing machine; a second cutting process to cut the pre-neck part of the forged mold product by using a second cutter of the ball stud processing machine, to shape the neck part and the washer part; and a surface finishing/burnishing process to finish/burnish the ball-shaped head part by using a surface finishing/burnishing tool of the ball stud processing machine.

The cutting and surface finishing/burnishing step is performed by the ball stud processing machine comprising: a holding unit in which a chuck is rotatably connected to a headstock, jaws are mounted on the front of the chuck such that a holding groove to receive and hold the ball stud is formed at the center of the chuck; and a tool unit in which a turret is connected to a main body enabling a position change, a plurality of attachment apertures are formed in the front of the turret such that the first cutter, the second cutter and the surface finishing/burnishing tool are securely held in the attachment apertures, respectively.

The surface finishing/burnishing tool of the tool unit comprises: a tool holder to be mounted in the attachment aperture of the turret; a carbide wheel to finish/burnish the surface of the ball-shaped head part of the forged mold product; and a shaft to connect the tool holder and the carbide wheel.

The ball stud processing machine further comprises: a control unit controlling the holding unit and the tool unit simultaneously to operate a first driving unit and a second driving unit, the first driving unit operates a motor to drive the holding unit such that the holding unit rotates as programmed, and the second driving unit operates a motor to drive the tool unit such that the tool unit changes in operative position in order of the first cutter to cut the ball-shaped head part, the second cutter to cut the pre-neck part and the surface finishing/burnishing tool to process the surface finishing/burnishing of the ball-shaped head part as programmed.

Advantageous Effects

According to the method for manufacturing a stainless steel ball stud for an automotive suspension system of the present invention, productivity is improved and manufacturing costs are reduced since the method enables to easily manufacture the stainless steel ball stud which is shaped with a ball-shaped head part, a recessed neck part under the head part, a washer part at a lower end of the neck part, a straight line part under the washer part and having a smaller diameter than the washer part, a tapered part under the straight line part and having a diameter which gradually becomes smaller downwardly, a male thread part under the tapered part and having a smaller diameter than the lower end of the tapered part, a dog point part under the male thread part and having a smaller diameter than the male thread part, and a hex socket formed into the bottom of the dog point part.

Further, since the hex socket is alone separately shaped at the forging and molding step, the precision of the hex socket is greatly improved to manufacture a high quality stainless steel ball stud for an automotive suspension system.

Further, since the tapered part is shaped during the last one-time molding process at the forging and molding step, the tapered part is precisely shaped and therefore any post-processes for the tapered part are not required, thereby reducing the number of processes, improving productivity and reducing costs.

Further, since the cutting of the head part and the neck part and the surface finishing/burnishing of the head part are performed by using one ball stud processing machine at the cutting and surface finishing/burnishing step, the productivity is improved and manufacturing costs are reduced.

Further, since the heat-treatment step to improve rigidity and the plating step to prevent the surface corrosion are skipped, the stainless steel ball stud is more easily manufactured and therefore productivity is improved and manufacturing costs are reduced.

DESCRIPTION OF DRAWINGS

These and other aspects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiment(s), taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a front view of a stainless steel ball stud for an automotive suspension system related to the present invention;

FIG. 2 is a flow chart of a method for manufacturing a stainless steel ball stud for an automotive suspension system according to the present invention;

FIG. 3a through 3f are cross-sectional views of main parts during each molding process at a forging and molding step in the method for manufacturing a stainless steel ball stud according to the present invention;

FIG. 4a through 4f are front views of a mold product during each molding process at the forging and molding step in the method for manufacturing a stainless steel ball stud according to the present invention;

FIG. 5 is a block diagram of a ball stud processing machine used at a cutting and surface finishing/burnishing step in the method for manufacturing a stainless steel ball stud according to the present invention;

FIG. 6 is a perspective view of main parts of a holding unit of the ball stud processing machine;

FIG. 7 is a perspective view of main parts of a tool unit of the ball stud processing machine;

FIG. 8 is a partial cross-sectional view of a surface finishing/burnishing tool of the ball stud processing machine; and

FIGS. 9a and 9b show a carbide wheel of the surface finishing/burnishing tool of the ball stud processing machine.

MODE FOR INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawing(s), in which preferred embodiments of the invention are shown

It should be understood that, the terms of directional indication, such as, “upward”, “downward”, “forward”, “backward”, etc., are defined based on the states illustrated in the drawings.

The present invention relates to a method for manufacturing a stainless steel ball stud 10 for an automotive suspension system as shown in FIG. 1, among ball studs in various shapes. The stainless steel ball stud 10 is in a shape with a head part 11 in a ball shape, a recessed neck part 12 under the head part 11, a washer part 13 at a lower end of the neck part 12, a straight line part 14 under the washer part 13 and having a smaller diameter than the washer part 13, a tapered part 15 under the straight line part 14 and having a diameter which gradually becomes smaller downwardly, a male thread part 16 under the tapered part 15 and having a smaller diameter than the lower end of the tapered part 15, a dog point part 17 under the male thread part 16 and having a smaller diameter than the male thread part 16, and a hex socket 18 formed into the bottom of the dog point part 17.

FIG. 2 is a flow chart of the method for manufacturing a stainless steel ball stud for an automotive suspension system according to the present invention.

The method for manufacturing a stainless steel ball stud according to the present invention comprises: a forging and molding step, a male thread shaping step and a cutting and surface finishing/burnishing step.

In the method according to the present invention, since a stainless steel material is used, a heat-treatment step to increase rigidity and a plating step to prevent surface corrosion are not needed after the forging and molding step.

In the forging and molding step, a material blank of a certain length and a cylindrical shape with the same top and bottom diameters is molded as a mold product having a shape which is similar to the shape of a final ball stud 10, by using a progressive press machine which simultaneously operates a number of mold dies and moves a forged mold product of a preceding die to a succeeding die.

The forging and molding step using the progressive press machine includes a six (6)-step molding process, such that the cut material blank is moved to a first mold die, a first mold product is moved to a second mold die, a second mold product is moved to a third mold die, a third mold product is moved to a fourth mold die, a fourth mold product is moved to a fifth mold die, a fifth mold product is moved to a sixth mold die, and a sixth mold product is discharged to the outside.

Since the multi-level progressive molding technique is obvious in the technical field to which the present invention belongs, no detailed description thereof is presented.

FIG. 3a through 3f are cross-sectional views of main parts during each molding process at the forging and molding step and FIG. 4a through 4f are front views of the mold product during each molding process at the forging and molding step.

In FIG. 3a , a first molding process is to level a top surface and a bottom surface of the cylindrical stainless steel material blank, which has a certain length and the same top and bottom diameters, by using a first mold die.

As shown in FIG. 4a , a first mold product 101 shaped through the first molding process has a vertical part 101 a in which the top diameter is the same as the bottom diameter and a lower end is rounded with a smaller diameter.

The total length of the first mold product 101 is slightly reduced in comparison with the total length of the material blank.

In FIG. 3b , a second molding process is to shape a pre-male thread part 102 a at a lower section of the vertical part 101 a of the first mold product 101 by using a second mold die. The pre-male thread part 102 a is in a vertical shape and has a smaller diameter than the vertical part 101 a.

As shown in FIG. 4b , in a second mold product 102 shaped through the second molding process, the vertical part 101 a with a relatively greater diameter and the pre-male thread part 102 a with a relatively smaller diameter are connected to each other in a hemispheric shape.

The total length of the second mold product 102 extends in comparison with the total length of the first mold product 101, and the length of the pre-male thread part 102 a is about ¼ of the total length of the second mold product 102.

In FIG. 3c , a third molding process is to shape a pre-head part 103 a and a pre-neck part 103 b in a upper section of the vertical part 101 a of the second mold product 102 by using a third mold die.

As shown in FIG. 4c , in a third mold product 103 shaped through the third molding process, the pre-head part 103 a is tapered such that its lower diameter is bigger than its upper diameter; the pre-neck part 103 b positioned between the pre-head part 103 a and the vertical part 101 a is in a vertical shape with a greater diameter than the vertical part 101 a. The diameter of a lower end of the pre-head part 103 a is greater than the diameter of the pre-neck part 103 b. Therefore, the pre-head part 103 a and the pre-neck part 103 b are tapered such that their diameters become gradually narrower downwardly.

The total length of the third mold product 103 is shorter than that of the second mold product 102 and longer than that of the first mold product 101.

The length of the vertical part 101 a in the third mold product 103 is greatly reduced in comparison with the length of the vertical part 101 a of the second mold product 102. The length of the pre-head part 103 a is similar to the length of the vertical part 101 a which has shortened.

In the third molding process, the connection part of the vertical part 101 a and the pre-male thread part 102 a is pressed. Accordingly, the length of the pre-male thread part 102 a of the third mold product 103 slightly extends, compared with the length of the pre-male thread part 102 a of the second mold product 102.

In FIG. 3d , a fourth molding process is to shape a ball-shaped head part 104 a_at the pre-head part 103 a of the third mold product 103, simultaneously to shape a vertical dog point part 104 b, which has a smaller diameter than the pre-male thread part 102 a, at a lower end section of the pre-male thread part 102 a of the third mold product 103, and simultaneously to shape a pre-hex socket part 104 c at a bottom of the dog point part 104 a, by using a fourth mold die.

As shown in FIG. 4d , in the fourth mold product 104 shaped through the fourth molding process, the pre-neck part 103 b, the vertical part 101 a, the pre-male thread part 102 a and the dog point part 104 b are positioned under the ball-shaped head part 104 a.

The pre-hex socket part 104 c positioned at the bottom of the dog point part 104 b of the fourth mold product 104 is recessed in an arc shape.

In the fourth molding process, since the pre-head part 103 a, which is tapered and is relatively longer in length, is pressed to be changed to the ball-shaped head part 104 a which is relatively shorter in length, the total length of the fourth mold product 104 is reduced in comparison with the total length of the third mold product 103.

In FIG. 3e , a fifth molding process to shape a hex socket 105 a at the bottom of the dog point part 104 b of the fourth mold product 104, by using a fifth mold die.

FIG. 4e is a front view of a fifth mold product 105 shaped through the fifth molding process.

In the fifth molding process, the hex socket 105 a is shaped by additionally pressing the pre-hex socket part 104 c positioned at the bottom of the dog point part 104 b of the fourth mold product 104.

Since the fifth molding process shapes the hex socket 105 a only, the hex socket 105 a is more precisely shaped.

The total length and exterior shape of the fifth mold product 105 shaped through the fifth molding process has no big change in comparison with the fourth mold product 104.

A sixth molding process is to shape a tapered part 106 a at a lower section of the vertical part 101 a of the fifth mold product 105, by using a sixth mold die.

FIG. 4f is a front view of a sixth mold product 106 shaped through the sixth molding process.

In the sixth molding process, since the lower section of the vertical part 101 a is relatively shorter in length, to extend to be changed as the tapered part 106 a which is relatively longer in length, the total length of the sixth mold product 106 extends in comparison with the total length of the third mold product 103.

As described above, the method according to the present invention manufactures the most proper forged mold product 106 for manufacturing the stainless steel ball stud 10 related to the present invention, through the forging and molding step including the first to sixth molding processes.

As shown in FIG. 4f , the sixth mold product 106, which is a final mold product made through the forging and molding step including the first to sixth molding processes, is shaped such that the pre-neck part 103 b in the vertical shape is positioned under the bell-shaped head part 104 a, the vertical part 101 a with the smaller diameter than the pre-neck part 103 b is positioned under the pre-neck part 103 b, the tapered part 106 a with the diameter becoming narrower downwardly is positioned under the vertical part 101 a, the pre-male thread part 102 a with the smaller diameter than the lower end of the tapered part 106 a is positioned under the tapered part 106 a, the dog point part 104 b with the smaller diameter than the pre-male thread part 102 a is positioned under the pre-male thread part 102 a, and the hex socket 105 a is positioned into the bottom of the dog point part 104 b.

Hereinafter, the forged mold product 106 means the sixth mold product 106 which is the final mold product manufactured through the forging and molding step.

The male thread shaping step is to shape a male thread at the pre-male thread part 102 a of the forged mold product 106 by using a rolling machine.

Since the male thread shaping technique is obvious in the technical field to which the present invention belongs, no detailed description thereof is presented.

The cutting and surface finishing/burnishing step is to cut the ball-shaped head part 104 a of the forged mold product 106 to exact dimensions to shape the head part 11, to cut the pre-neck part 103 to shape the neck part 12 and the washer part 13, and to perform the surface finishing/burnishing work to the head part 11, by using one ball stud processing machine 100, thereby completing the final stainless steel ball stud 10 for an automotive suspension system.

The cutting and surface finishing/burnishing step comprises: a first cutting process to cut the ball-shaped head part 104 a of the forged mold product 106 to exact dimensions by using a first cutter 310 of the ball stud processing machine 100; a second cutting process to cut the pre-neck part 103 b of the forged mold product 106 to shape the neck part 12 and the washer part 13 by using a second cutter 320 of the ball stud processing machine 100; and a surface finishing/burnishing process to finish/burnish the ball-shaped head part 104 a by using a surface finishing/burnishing tool 330 of the ball stud processing machine 100.

The second cutting process is to cut the upper portion of the pre-neck part 103 b to be recessed, except for a lower end of the pre-neck part 103 b of the forged mold product 106, so that the neck part 12 is shaped and the washer part 13 remains at the lower end of the neck part 12.

FIG. 5 is a block diagram of the ball stud processing machine 100 used at the cutting and surface finishing/burnishing step in the method for manufacturing a stainless steel ball stud according to the present invention, FIG. 6 is a perspective view of main parts of a holding unit of the ball stud processing machine 100, and FIG. 7 is a perspective view of main parts of a tool unit of the ball stud processing machine 100.

The ball stud processing machine 100 used at the cutting and surface finishing/burnishing step comprises: a holding unit 200 and a tool unit 300. In the holding unit 200, a chuck 204 is rotatably connected to a headstock 202, jaws 208 are mounted on the front of the chuck 204, a holding groove 208 to receive and hold the ball stud 10 is positioned at the center of the chuck 204. In the tool unit 300, a turret 304 is connected to a main body 302 enabling to change position, a plurality of attachment apertures 306 a, 306 b, 308 are formed in the front of the turret 304 such that the first cutter 310, the second cutter 320 and the surface finishing/burnishing tool 330 are secured in the attachment apertures 306 a, 306 b and 308, respectively.

In the ball stud processing machine 100, the surface finishing/burnishing tool 330 of the tool unit 300 comprises: a tool holder 332 to be mounted in the attachment aperture 308; a carbide wheel 334 connected to the tool holder 332 by a shaft 336; and a working fluid discharge hole 344 formed to penetrate the inside of the shaft 336.

The ball stud processing machine 100 performs all of the cutting processes and the surface finishing/burnishing process of the forged mold product 106 which finished the forging process.

That is, a control unit 420 controls the holding unit 200 and the tool unit 300 to be driven to process the forged mold product 106 after the forging step, such that the cutting process to cut the ball-shaped head part 104 a and the pre-neck part 103 b is primarily performed and then the surface finishing/burnishing process is secondarily performed to make a uniform average surface roughness of the head part 104 a within a predetermined range (for example, 01˜05a).

The holding unit 200 includes the headstock 202 which is a main body, the chuck 204 and a plurality of the jaws 206 directly securely holding the forged mold product 106.

As shown in FIG. 5, the headstock 202 of the holding unit 200 is connected to a first driving unit 430. As shown in FIG. 6, the holding groove 208 is formed at the front of the chuck 204 rotating at a speed required in the ball stud processing machine 100, by radially positioning the three (3) jaws 206 at evenly spaced intervals.

As shown in FIG. 7, the tool unit 300 includes the drum-shaped main body 302 and the disc-shaped turret 304. The turret 304 is provided with a plurality of the attachment apertures 306 a, 306 b, 308 to securely hold various tools.

Each of the attachment apertures 306 a, 306 b, 308 has a proper shape for each tool. The two attachment apertures 306 a, 306 b to hold the first cutter 310 and the second cutter 320 include fitting grooves, and the attachment aperture 308 to hold the surface finishing/burnishing tool 330 includes a through-hole.

As shown in FIG. 5, when an operation unit 410 is controlled and operated in the ball stud processing machine 100, the control unit 420 to control the holding unit 200 and the tool unit 300 operates the first driving unit 430 and second driving unit 440.

The first driving unit 430 operates a motor 450 a to drive the holding unit 200, so that the holding unit 200 rotates as programmed. The second driving unit 440 operates a motor 450 b of the tool unit 300, so that the tool unit 300 changes in operative position in order of the first cutter 310 to cut the ball-shaped head part 104 a, the second cutter 320 to cut the pre-neck part 103 b and the surface finishing/burnishing tool 330 to finish/burnish the surface of the ball-shaped head part 104 a as programmed.

During the cutting processes using the first and second cutters 310, 320, a cutting oil sprayer 600 separately structured to the outside sprays cutting oil to a cutting knife. During the surface finishing/burnishing process using the surface finishing/burnishing tool 330, the working fluid discharge hole 344 formed inside the surface finishing/burnishing tool 330 allows a suitable amount of a working fluid to release to the carbide wheel 334.

The surface finishing/burnishing tool 330 of the tool unit 300 has the most important function in determining the average surface roughness of the ball stud 10.

FIG. 8 is a partial cross-sectional view of the surface finishing/burnishing tool 330 of the ball stud processing machine 100, and FIGS. 9a and 9b show the carbide wheel 334 of the surface finishing/burnishing tool 330.

As shown in FIG. 8, the surface finishing/burnishing tool 330 of the tool unit 300 includes the tool holder 332 to be mounted onto the attachment aperture 308 of the turret 304, the carbide wheel 334, and the shaft 336 penetrating the tool holder 332 and the carbide 334 to connect the tool holder 332 and the carbide 334.

A bearing 338 is positioned between the shaft 336 inside the carbide wheel 334 and the carbide wheel 334. A washer 340 is positioned between the shaft 336 in the front and back of the carbide 334 and the tool holder 332.

A suitable amount of the working fluid is released to the carbide wheel 334 through the working fluid discharge hole 344 formed inside the shaft 336. A working fluid inlet 342 with a sealing lid is provided at the other side to an outlet of the working fluid discharge hole 342.

In the surface finishing/burnishing tool 330, forming the radius R of the outer circumference of the carbide wheel 334 is very important since the size of the radius R determines a contact rate of the carbide wheel 334 and the head part 11 of the ball stud 10.

If the radius R of the outer circumference of the carbide wheel 334 is too small, the contact rate is low so that the time for surface finishing/burnishing is long. If the radius R of the outer circumference of the carbide wheel 334 is too large, the contact rate is high so that a stripe occurs in the head part 11 and the surface roughness is increased.

The radius R of the outer circumference of the carbide wheel 334 of the surface finishing/burnishing tool 330 is preferable within 15˜3 mm. In the surface finishing/burnishing process, preferably, the average surface roughness of the head part 11 of the ball stud 10 is 01˜05a.

The invention has been described using preferred exemplary embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed embodiments. On the contrary, the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. The scope of the claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A method for manufacturing a stainless steel ball stud for an automotive suspension system, in which the stainless steel ball stud (10) is shaped with a head part (11) in a ball shape, a recessed neck part (12) under the head part (11), a washer part (13) at a lower end of the neck part (12), a straight line part (14) under the washer part (13) and having a smaller diameter than the washer part (13), a tapered part (15) under the straight line part (14) and having a diameter which gradually becomes narrower downwardly, a male thread part (16) under the tapered part (15) and having a smaller diameter than the lower end of the tapered part (15), a dog point part (17) under the male thread part (16) and having a smaller diameter than the male thread part (16), and a hex socket (18) formed into a bottom of the dog point part (17), the method comprising: a forging and molding step of forging and molding a cylindrical shaped stainless material blank with the same top and bottom diameters by using a progressive press machine to operate a number of mold dies simultaneously and to move a forged mold product of a preceding die to a succeeding die, to make a forged mold product (106); a male thread shaping step of shaping a male thread on the forged mold product (106); and a cutting and surface finishing/burnishing step of cutting the forged mold product (106) by using one ball stud processing machine (100) such that the head part (11) is cut at exact dimensions, the neck part (12) and the washer part (13) are shaped and the surface finishing/burnishing work to the head part (11) is performed to complete the stainless steel ball stud (10) for an automotive suspension system.
 2. The method for manufacturing a stainless steel ball stud according to claim 1, characterized in that the forging and molding step manufactures the forged mold product (106) which is shaped with a ball-shaped head part (104 a), a pre-neck part (103 b) arranged in a vertical shape under the ball-shaped head part (104 a), a vertical part (101 a) under the pre-neck part (103 b) and having a smaller diameter than the pre-neck part (103 b), a tapered part (106 a) under the vertical part (101 a) and having a diameter which becomes gradually narrower downwardly, a pre-male thread part (102 a) under the tapered part (106 a) and having a smaller diameter than a lower end of the tapered part (106 a), a dog point part (104 b) under the pre-male thread part (102 a) and having a smaller diameter than the pre-male thread part (102 a), and a hex socket (105 a) at the bottom of the dog point part (104 b).
 3. The method for manufacturing a stainless steel ball stud according to claim 2, characterized in that the forging and molding step comprises a six (6)-step molding process such that the cut material is moved to a first mold die, a first mold product (101) is moved to a second mold die, a second mold product (102) is moved to a third mold die, a third mold product (103) is moved to a fourth mold die, a fourth mold product (104) is moved to a fifth mold die, a fifth mold product (105) is moved to a sixth mold die, and a sixth mold product (106) is discharged to the outside.
 4. The method for manufacturing a stainless steel ball stud according to claim 3, wherein the forging and molding step comprises: a first molding process to mold, in a first mold die, a first mold product (101) that includes the generally vertical part (101 a) with a top and bottom having the same diameter, and a rounded bottom end with a smaller diameter, by using the material blank of a certain length which has a top end and a bottom end with the same diameter; a second molding process to mold, in a second mold die, a second mold product (102) in which the pre-male thread part (102 a) positioned at a lower section of the vertical part (101 a) is in a vertical shape with a smaller diameter than the vertical part (101 a) and the vertical part (101 a) is connected to the pre-male thread part (102 a) in a hemispheric shape, by using the first mold product (101); a third molding process to mold, in a third mold die, a third mold product (103) in which a pre-head part (103 a), which is tapered to have an upper end with a greater diameter than a lower end, and the pre-neck part (103 b), which is in a vertical shape with a greater diameter than the vertical part (101 a), are positioned in an upper section of the vertical part (101 a), and the pre-head part (103 a) and the pre-neck part (103 b) are connected to be tapered such that a diameter becomes narrower downwardly, by using the second mold product (102); a fourth molding process to mold, in a fourth mold die, a fourth mold product (104) in which the ball-shaped head part (104 a) is shaped in the pre-head part (103 a), the dog point part (104 b) in a vertical shape with a smaller diameter than the pre-male thread part (102 a) is shaped in a lower section of the pre-male thread part (102 a) and a pre-hex socket part (104 c) is shaped at a lower end of the dog point part (104 b), by using the third mold product (103); a fifth molding process to mold, in a fifth mold die, a fifth mold product (105) in which the hex socket (105 a) is shaped at the lower end of the dog point part (104 b), by using the fourth mold product (104); and a sixth molding process to mold, in a sixth mold die, a sixth mold product (106) in which the tapered part (106 a) is shaped in a lower section of the vertical part (101 a), by using the fifth mold product (105).
 5. The method for manufacturing a stainless steel ball stud according to claim 1, wherein the cutting and surface finishing/burnishing step comprises: a first cutting process to cut the ball-shaped head part (104 a) of the forged mold product (106) at exact dimensions to shape the head part (11) by using a first cutter (310) of the ball stud processing machine (100); a second cutting process to cut the pre-neck part (103 b) of the forged mold product (106) by using a second cutter (320) of the ball stud processing machine (100), to shape the neck part (12) and the washer part (13); and a surface finishing/burnishing process to finish/burnish the ball-shaped head part (104 a) by using a surface finishing/burnishing tool (330) of the ball stud processing machine (100).
 6. The method for manufacturing a stainless steel ball stud according to claim 5, wherein the cutting and surface finishing/burnishing step is performed by the ball stud processing machine (100) comprising: a holding unit (200) in which a chuck (204) is rotatably connected to a headstock (202), jaws (206) are mounted on the front of the chuck (204) such that a holding groove (208) to receive and hold the ball stud (10) is formed at the center of the chuck (204); and a tool unit (300) in which a turret (304) is connected to a main body (302) enabling a position change, a plurality of attachment apertures (306 a)(306 b)(308) are formed in the front of the turret (304) such that the first cutter (310), the second cutter (320) and the surface finishing/burnishing tool (330) are securely held in the attachment apertures (306 a)(306 b)(308), respectively.
 7. The method for manufacturing a stainless steel ball stud according to claim 6, wherein the surface finishing/burnishing tool (330) of the tool unit (300) comprises: a tool holder (332) to be mounted in the attachment aperture (308) of the turret (304); a carbide wheel (334) to finish/burnish the surface of the ball-shaped head part (104 a) of the forged mold product (106); and a shaft (336) to connect the tool holder (332) and the carbide wheel (334).
 8. The method for manufacturing a stainless steel ball stud according to claim 6, wherein the ball stud processing machine (100) further comprises: a control unit (420) controlling the holding unit (200) and the tool unit (300) simultaneously to operate a first driving unit (430) and a second driving unit (440), the first driving unit (430) operates a motor (450 a) to drive the holding unit (200) such that the holding unit (200) rotates as programmed, and the second driving unit (440) operates a motor (450 b) to drive the tool unit (300) such that the tool unit (300) changes in operative position in order of the first cutter (310) to cut the ball-shaped head part (104 a), the second cutter (320) to cut the pre-neck part (103 b) and the surface finishing/burnishing tool (330) to process the surface finishing/burnishing of the ball-shaped head part (104 a) as programmed. 